2.0s cylinders - black markings on inner bore??

[gilbert911]

I recently aquired a 68s 2.0ltr engine - typ 901/02 serial 4080xx
It's one of the early '68 MY engines with the alu case.
We started to strip it down for a re-build yesterday.
Generally all seems good condition..
some of the cylinders have black deposits / markings on the inner bore..

Can anyone help with what might be the cause of this ?
Any remedies so I can rebuild with confidence.
I'd like to re-use the barrells if at all possible.
The rebuild plans are stock/stock.
Many thanks for opinions
Pics of 2 of the cylinders effected....

[docrodg]

interesting, there are 2 possibilities off the top of my head. A carbon deposit, maybe from the engine overheating after it had excess buildup??? Bores are cast iron on those engines. Does it come off with a light scrape? That would be carbon deposits. If you had not said that the you stripped down the engine I would be tempted to say it was rust that had been treated with naval jelly. Of course, it could be that the engine had sat, rusted a bit in the bores, then been run or at least turned over and the rust was scraped off leaving behind the "Stain" of the affected metal which is still corroded just not red. I have seen that happen in cylinders before, the rings scrape off the rust but the sub-surface damage stays and looks like these pics. If rust then you need to hone the cylinders with stones and pray... if it goes deeper than you can hone then you will not be able to reuse the pistons as iron oxide is tougher than cast iron and will eat the rings up as well as the pistons.

[BURN-BROS]

It is most probably rust stains.

[matt demaria]

It is electrolysis corrosion from the aluminum/iron interface. Must be honed (if wear limits ok) for rings to seat.

[304065]

Gilbert, if you can't remove it with a scotch-brite pad lubricated with motor oil then you're looking at a re-bore. I had my Biral 80's bored to 81 and some custom JE pistons with a 9,5 compression ratio made up. Not only is this original appearing, but it's signifcantly less expensive than new Mahle Nikasil 80s. Also, I wanted a bump in compression but only went as high as 9,5 to work better with the reformulated Panther Pee sold to an unsuspecting consumer as "gasoline."

Details here: Good luck and you will find all the answers to your 2,0 questions on the forum.

Jugs and Slugs: Confessions of a JE Piston owner

[gilbert911]

Thanks guys for the replies - appreciate it very much..
'DocR' is on to something I think...
The engine had been sitting in a garage in Europe for certain 12 months - possibly 18 or more before it came to me. I had not been run in that time/
When we stripped it yesterday it was full of oil.
We had hand turned it prior to stripping.
Is that what's done it? Sounds like it might be it.
So to be clear -we look to hone and see if we clear it - if no luck then a re-bore right?
If the honing does do the job then would the existing cylinders with new rings be fine?
I have seen threads before where a certain manf. of rings get's mentioned as being the way to go if the cylinders are a little high on tolorence - Goertze or something like that ?

[tom1394racing]

I've seen the same issue several times on the early birals.

I hone them using a scotchbrite wheel and lapping compound. They quite often will clean up very nicely. If you can feel the defects with your fingernail after honing then they are probably not reusable.

The final check is to measure the bores for wear, taper and ovality with a dial bore gage.

[docrodg]

Originally Posted by gilbert911

Thanks guys for the replies - appreciate it very much..
'DocR' is on to something I think...
The engine had been sitting in a garage in Europe for certain 12 months - possibly 18 or more before it came to me. I had not been run in that time/
When we stripped it yesterday it was full of oil.
We had hand turned it prior to stripping.
Is that what's done it? Sounds like it might be it.
So to be clear -we look to hone and see if we clear it - if no luck then a re-bore right?
If the honing does do the job then would the existing cylinders with new rings be fine?
I have seen threads before where a certain manf. of rings get's mentioned as being the way to go if the cylinders are a little high on tolorence - Goertze or something like that ?

y/w. Yes, hand cranking probably scraped the rust off, but again, the dark spots are still iron oxide too. Measure the cylinders for wear, taper, oval, etc. and the pistons for size and determine if they can be honed, do not go over the specified tolerance, measure after the hone and see if you are still ok. If not bore out and buy some JE pistons.